For concurrent-use licenses: Stop the License Manager service (License Server Administrator > Start/Stop License Service) and close the License Server Administrator.
For single-use licenses: Close the ArcGIS Administrator.
Navigate to the FLEXnet folder. The locations of the trusted storage on a Windows machine for concurrent-use and single-use are as follows:
Windows XP and 2003 Server:
C:\Documents and Settings\All Users\Application Data\FLEXnet
Windows Vista, 7, 8, Server 2008, Server 2012:
Location of the trusted storage on a UNIX/Linux machine for concurrent-use:
Either remove all of the ArcGIS_xxxxxxxx_tsf.data files within the FLEXNet folder, or create a new folder and move the files into the new folder. Make sure to remove the ArcGIS_xxxxxxxx_tsf.data files from the FlexNet folder.
Verify that the licenses are removed.
For concurrent-use licenses, start the License Manager service (License Server Administrator > Start/Stop License Service) and close the License Server Administrator. Click the Availability folder to verify it has been cleared.
For single-use licenses, open the ArcGIS Administrator and click the Availability folder.